Antenna Tuners....Yea or Nay?

[W5LZ]

For what it's worth, I don't agree with WC7I's explanation. I think he's made a false inference from an assumption. At the beginning of the information on the site given he says, "This makes the antenna appear to be resonant, and coax #2 becomes the correct electrical length for re-reflections to happen.", speaking about the tuner. While it's 'true' if you are speaking about what the transmitter thinks it 'sees' looking into the tuner. The problem with that is that there has been no change in the mismatch between feed line and antenna (which is at the junction of those two things). The required reactances furnished by the tuner to 'correct' that mismatch is being applied in the wrong place. Sure, it makes the transmitter think everything is "tuned" so it puts out what it would into a tuned system, it doesn't reduce/'cut-back' because of SWR. The end result will be that more power will reach that antenna than without the tuner, but it won't be as much power as a correctly matched system would result in. [When you stop and think about it, that's a pretty good reason for using a tuner with a non-resonant and correctly matched antenna! Right?]
Now, if that tuner were placed at the feed point of that antenna where the typical impedance mismatch occurs... But that isn't very easy to do, requires sort'a long arms to tune that tuner (or remote control of that tuner). It also introduces several other "not so easy" practical aspects. Such as doing that remote tuning, the size/weight of the tuner at the feed point, and who knows what else. There are certainly a few of those type 'tuners' around, but they aren't simple, easy, or cheap.
A tuner at the transmitter end of the feed line can certainly make a not so good antenna usable, and quite a few people use them (including me). It's 'better', but it's certainly not the 'best' way of doing it.
- 'Doc

There's another 'myth' or misunderstanding quoted on WC7I's site that I think would be a good thing to remember. That is that reflected power never get's back into your radio and burns thing up. The reason why things may fail when you have reflected power (high SWR) is because the transmitter is trying to work into a wrong 'sized' load. You can make a 1/2 horse power motor spin a huge ferris wheel, but only if the load presented to that motor is 'matched' correctly with the proper gearing. A tuner is a lot like a transmission. And then you gotta shift the thing...

 

[Kamikaze]

What Maxwell wrote is simple and true. An antenna coupler redirects the reflected energy toward the load. Almost all energy is radiated.

This holds true if the coupler is not used at extremes of its capability into open wire line.

Coils get hot and melt when the coupler is mis-used.

The very popular high pass T network with a 4:1 balun on its output will tune with a number of different combinations. Always use the one with the most capacitance. Other settings will sacrifice power to component loss due to high circulating current.

Next problem is the 4:1 output balun. Whenever the impedance seen by the coupler is less than 300 - 400 ohms ignoring j, the coupler is probably going to transfer more power to the antenna using a 1:1 "current" balun.

Even short antennas like the 40 meter dipole being tried on 80 meters mentioned here will work very well with a coupler capable of sourcing lower impedances OR enough feedline to transform the impedance to something a garden variety "tuner" will handle. The rules are different however. Conductor sizes become important. The antenna itself and feeders must be made with larger wire because with low impedances current is high.

I know a half dozen people on 160 meters who use 160 foor center fed antennas made with #8 wire nead the center and #8 or larger feeders. Most of these people are using the Measures balanced balanced tuner. They all are QRO.

Plenty of internet gurus make mistakes. There are even guru wars on the amps reflector and QRZ. Nobody can be correct all the time. Discounting someone's writings which have stood the test of time due to a couple mistakes made on some ham site is throwing the baby out with the bath water.

 

[wavrider]

Been there and done that. While both Cebik and Maxwell are authorities on the subject both have been proven to be wrong on the odd occasion as well.I have actually engaged W2DU on several occassions on this subject on amphone.net. My comments were directed at what YOU posted,not what Cebik or Maxwell said. YOU said tuners do not generate heat. I said false. While they do not generate heat of their own accord they do in fact heat up due to losses in the inductor therefore tuners do produce heat.That is a fact. ask almost any ham that runs high power and uses a tuner.Moleculoe deformed the coil in his tuner due to heat.YOU also said that you will actually get more power out to the antenna than the transmitter produces. I don't know how to break it to you but that is an impossibility. You cannot create energy from nothing. Combining forward and reflected power does not equal more power than the transmitter produces.

Place a power meter before the coupler, the same brand make model behind the coupler, key a carrier unmodulated into the system, say 10 watts, if the coupler is tuned it will show a 10 watt carrier into the input of the coupler, then read the power out at the watt meter placed on the output of the coupler and before the antenna and feed line, that watt meter will read a higher power out than the meter on the input.

How is that, it is the same 10 watt carrier on the input as the output of the coupler, where is that higher wattage reading coming from? The coupler is not an amplifier.

 

[Captain Kilowatt]

Power meters do not read power directly. They measure RF voltage and display that on a scale calibrated in watts based on a 50 ohm load. Since the load on the meter before the coupler is 50 ohms and the load after the coupler is not 50 ohms they will show different levels even though they may still have the same amount of power flowing through them. This is because the loads are different and therefore the applied RF voltage to those loads MUST be different in order to maintain the same power level.

 

[BOOTY MONSTER]

You think if you are experimenting with home brew antennas...it would be worth buying a tuner?

nope . you only have half a MHz bandwidth for the cb band .
id also cut the dipoles a few inches longer on each end and then cut it to tune best rather than useing a set length that's supposed to work .

 

[Eastside]

nope . you only have half a MHz bandwidth for the cb band .
id also cut the dipoles a few inches longer on each end and then cut it to tune best rather than useing a set length that's supposed to work .

Now I am thinking about a moonraker 4 my buddy offered me for a $100....I bet I could talk some skip on that monster.

 

[BOOTY MONSTER]

oh yea

 

[Kamikaze]

Place a power meter before the coupler, the same brand make model behind the coupler, key a carrier unmodulated into the system, say 10 watts, if the coupler is tuned it will show a 10 watt carrier into the input of the coupler, then read the power out at the watt meter placed on the output of the coupler and before the antenna and feed line, that watt meter will read a higher power out than the meter on the input.

How is that, it is the same 10 watt carrier on the input as the output of the coupler, where is that higher wattage reading coming from? The coupler is not an amplifier.

Not all power meters work the same way.

The Bird 43 adds reflected power to the forward power reading. It is possible to read almost 200 watts forward power at the output of a 100 watt transmitter.

 

[W5LZ]

Kamikaze,
I'm afraid you're mistaken about that '43. It doesn't add the reflected to the forward power reading, you have to do that. As far as 'spoofing' a watt meter, sure, you can do that with any of them. It's a matter of not understanding exactly what they are telling you.
- 'Doc

 

[Kamikaze]

Kamikaze,
I'm afraid you're mistaken about that '43. It doesn't add the reflected to the forward power reading, you have to do that. As far as 'spoofing' a watt meter, sure, you can do that with any of them. It's a matter of not understanding exactly what they are telling you.
- 'Doc

No need to be afraid. It is right in the manual.

 

[W5LZ]

I don't have a manual so how about copying that section here?
- 'Doc

 

[Kamikaze]

Plug "bird 43 manual" into a search engine. Excellent bedtime reading.

 

[W5LZ]

I just read that manual and can't find anything about a '43' adding reflected and forward power. The user of that meter has to do that. I'd also recommend taking a look at an explanation of "incident power", that may help some.
It's certainly possible for a watt meter to do that 'adding'/'subtracting', but it means it isn't a $imple watt meter anymore, and is still open to huge errors from misuse or misunderstandings.
It amounts to knowing what you got and how to use it.
- 'Doc

 

[Kamikaze]

I just read that manual and can't find anything about a '43' adding reflected and forward power. The user of that meter has to do that. I'd also recommend taking a look at an explanation of "incident power", that may help some.
It's certainly possible for a watt meter to do that 'adding'/'subtracting', but it means it isn't a $imple watt meter anymore, and is still open to huge errors from misuse or misunderstandings.
It amounts to knowing what you got and how to use it.
- 'Doc

Read it again you missed it.

Got a Bird 43? Try it for yourself. Put a known wattage into a 50 ohm load. Replace the load with a 100 200 or 300 ohm resistor. Read forward power. It will increase. Read reflected power. Notice the forward power increase is the amount read for reflected power.

Anyone out there with an antenna tuner want to play along? Mess up your SWR on purpose and tell us what your Bird does.

 

[W5LZ]

Oh ho! Now I see. You're talking about intentional misuse. It's also a good thing you picked a larger size of mismatch. Otherwise, it wouldn't be worth the effort. You still have to know two of the three variables in that equation, not very likely.
- 'Doc